Summary. This study was aimed to develop an approach allowing pain behavior estimation of rats with experimental endometriosis. The histological score was design to assess the degree of changes observed in the endometrial tissues. Experimental endometriosis was carried out on anesthetized sexually mature intact females of outbred rats aged 10–11 weeks by autotransplantation of a segment of the horn of the uterus. Implant was placed between the peritoneum and muscle. The pain behavior was estimated 2, 4 and 8 weeks after surgery. Sensitivity to abdominal probing was assessed by pressing the lower abdomen against a rod attached to a gram force meter, and measuring the force producing withdrawal/escape behaviors. The pain response to the mechanical stimulation of the abdominal wall was significantly higher in the animals with endometriosis compared to the sham-operated rats. 50% of the animals was euthanatized 4 weeks after the pathology induction, 50% – after 8 weeks. A morphological study indicated the presence of endometriotic-like implants exceeding in size of implanted segments. The histological examination showed morphological changes indicating endometriosis development. The ectopic endometrium was characterized by the coexistence of both glands and stromal structures. Glandular epithelia were observed to have an appearance similar to that of the eutopic epithelial glands. The degree of pathological changes was estimated using specially design grading system (score range – 0–3). As a result the approach for both histological evaluation and pain behavior assessment in rats with experimental endometriosis was developed. This model can be used to study the pharmacological action of new medicines.
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